Transport frame structure for retransmission in DSL

ABSTRACT

Included are embodiments for retransmission in a digital subscriber line environment. At least one embodiment of a method includes framing data into transport frames, each transport frame carrying payload data that is viewed differently according to the computing layer in which it is transported; transporting the transport frames over a first computing layer, the payload data of each transport frame corresponding to an integer number Q of elementary cells of the first computing layer, an integer number of header bytes containing information specific to the transport frame, and an integer number of padding bytes; and transporting the transport frames over a second computing layer, the payload data content of each transport frame corresponding to payload data of an integer number M of elementary cells of the second computing layer.

CROSS REFERENCE

This application claims priority to U.S. provisional applicationentitled, “Systems and Methods for Retransmission with ADSL2 UsingATM-TC,” having Ser. No. 61/145,680, filed Jan. 19, 2009, which isentirely incorporated herein by reference.

Also incorporated by reference are U.S. application Ser. No. 12/573,742,filed Oct. 5, 2009, entitled “Packet Retransmission Method for DSLSystems” and U.S. application Ser. No. 12/620,832 (Now U.S. Pat. No.8,413,000), filed Nov. 18, 2009, entitled “Retransmission above theGamma Interface.”

BACKGROUND

In asymmetric digital subscriber line (ADSL) and very high speed digitalsubscriber line (VDSL) environments, a retransmission (ReTx) techniquemay be utilized for ensuring quality of transmission forlatency-insensitive data, such as video.

The retransmission scheme used in xDSL systems supports (with smallvariations) both asynchronous transfer mode (ATM) and packet transfermode (PTM) protocols and has been designed such that elementary framesthat can be retransmitted are formed in the physical layer (PHY). It isalso proposed that for ADSL, retransmission is only used for thedownlink, whereas for VDSL, retransmission can be used either for thedownlink only or for both uplink and downlink.

A transmitter supporting the retransmission scheme implements aretransmission queue for storage of elementary frames in order to haveaccess to previously sent elementary frames in the event that a requestfor retransmission is received. A receiver supporting retransmissionscheme implements a rescheduling queue that resequences elementaryframes in the event that elementary frames are received out of order dueto retransmission.

Management of the retransmission queue (at the transmitter) and therescheduling queue (at the receiver) can be done in various layers ofthe xDSL PHY, including the transport protocol specific transmissionconvergence (TPS-TC) layer and the physical media specific transmissionconvergence (PMS-TC) layer. However, existing retransmission techniquesproposed so far assume that both retransmission queue and reschedulingqueue are implemented in the same layer.

SUMMARY

Included are embodiments for retransmission in a digital subscriber lineenvironment. At least one embodiment of a method includes framing datainto transport frames, each transport frame carrying payload data thatis viewed differently according to the computing layer in which it istransported; transporting the transport frames over a first computinglayer, the payload data of each transport frame corresponding to aninteger number Q of elementary cells of the first computing layer, aninteger number of header bytes containing information specific to thetransport frame, and an integer number of padding bytes; andtransporting the transport frames over a second computing layer, thepayload data content of each transport frame corresponding to payloaddata of an integer number M of elementary cells of the second computinglayer.

Also included are embodiments of a system. At least one embodiment of asystem includes a transmitter side device that includes: a firstcomputing layer transporting first layer transport frames, the firstlayer transport fames including payload data, the payload data of eachtransport frame corresponding to an integer number Q of elementary cellsof the first computing layer, an integer number of header bytescontaining information specific to the transport frame, and an integernumber of padding bytes, and a second computing layer transportingsecond format transport frames, the payload data content of each secondformat transport frame corresponding to an integer number M ofelementary cells of the second computing layer,

Other systems, methods, features, and advantages of this disclosure willbe or become apparent to one with skill in the art upon examination ofthe following drawings and detailed description. It is intended that allsuch additional systems, methods, features, and advantages be includedwithin this description and be within the scope of the presentdisclosure.

BRIEF DESCRIPTION

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views. While several embodiments are described inconnection with these drawings, there is no intent to limit thedisclosure to the embodiment or embodiments disclosed herein. On thecontrary, the intent is to cover all alternatives, modifications, andequivalents.

FIG. 1 illustrates an exemplary embodiment of retransmission scheme on asingle link.

FIG. 2A illustrates a transmitter reference model for a DSLretransmission method with the retransmission queue implemented in theTPS-TC layer.

FIG. 2B illustrates a receiver reference model for a DSL retransmissionmethod, with a rescheduling queue implemented in the TPS-TC layer.

FIG. 3A illustrates a transmitter reference model for a DSLretransmission method with the retransmission queue implemented in thePMS-TC layer.

FIG. 3B illustrates a receiver reference model of a DSL retransmissionmethod with a rescheduling queue implemented in the PMS-TC layer.

FIG. 4A illustrates a frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes as tail bytes at theend of the frame.

FIG. 4B illustrates a frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes at the beginning ofthe frame, after the header bytes.

FIG. 4C illustrates a frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes at both thebeginning and end of the frame, after the header bytes.

FIG. 5 illustrates an example process that may be utilized forretransmission of data between a plurality of devices.

DETAILED DESCRIPTION

Included herein are embodiments that define a transparent transportstructure for a retransmission scheme in xDSL that allows management ofthe rescheduling queue (at the receiver) either in the PMS-TC layer orthe TPS-TC layer independently of the location (PMS-TC or TPS-TC) of themanagement of the retransmission queue at the transmitter. This means anxDSL modem that performs retransmission with a queue management in thePMS-TC layer can support retransmission with a modem that performsmanagement in the TPS-TC layer, and vice versa.

Referring now to the drawings, FIG. 1 depicts the functional blockdiagram of the ReTx scheme on a single link. At the transmitter 102, aDTU framer 104 constructs the elementary frames, called data transmitunits (DTUs) that can be requested for retransmission. Each DTU containssome data provided by the transport protocol specific transmissionconvergence (TPS-TC) layer and some retransmission (ReTx) specificoverhead (that is further described in the following). The content ofeach DTU is stored in a so-called retransmission (ReTx) queue 106 priorto be transmitted over the retransmission forward channel (RFC)represented by the solid arrow path in FIG. 1. The storage of a DTUinvolves storing at least the data content of the DTU but also some (orall) ReTx specific overhead bytes. The transmitter 102 also receives,request messages on a so-called retransmission return channel (RRC)represented in the thickly dashed arrow path in FIG. 1. The receivedrequest messages (also called RRC messages) contain information on whichDTUs have been correctly received and which DTUs need to beretransmitted. For improved robustness while transmitted over the RCC,the request information may be coded on a specific format with a requestencoder 114, and hence may need some decoding with a request decoder 108in order to be correctly interpreted by the system.

At the receiver side 110, each DTU is checked for errors after receptionat a DTU error detector 111. Then, correct DTUs are passed to a higherlayer. When a DTU is corrupted, a request for retransmission isgenerated by a request encoder 114 and sent on the RRC. When aretransmission is in process, correctly received DTUs may need to bestored locally in a rescheduling queue 116 before being passed to higherlayer. Such storage ensures a correct ordering of the data passed to thehigher layer. The rescheduling queue 116 then acts as a buffer thatreschedules (or resequences) DTUs received out-of-sequence.

In many solutions such as the one illustrated in FIG. 1, for theretransmission scheme to work properly, the ReTx queue 106 at thetransmitter 102 and the rescheduling queue 112 must be implemented in alayer that can easily detect boundaries of each DTU for storage.

Two possible layers in which the queues may be implemented are theTPS-TC layer and the PMS-TC layer. However, the DTU may have differentstructures whether the scheme is implemented in the TPS-TC layer or thePMS-TC layer.

In the following, we propose a DTU structure designed such that atransmitter may implement the retransmission queue in a layer that isdifferent than the layer in which a receiver may implement itsrescheduling queue. This means a modem that performs retransmission witha queue management in the PMS-TC layer will support retransmission witha modem that performs management in the TPS-TC layer, and vice versa.

FIG. 2A illustrates a transmitter reference model for a DSLretransmission method with the retransmission queue implemented in theTPS-TC layer. As illustrated, the operations of the modem are splitbetween the PMS-TC (physical medium specific transmission convergence)layer 208 and TPS-TC (transport protocol specific transmissionconvergence) layer 204.

As illustrated in the nonlimiting example of FIG. 2A, data (e.g., ATM orPTM packets) may be received from an upper layer above the gammainterface 202. The selected data may then be sent across a gamma (γ)interface 202 and received at the TPS-TC layer 204 at a DTU framercomponent 206. The DTU framer component 206 reformats the received datainto one or more DTUs. The DTU framer component 206 can also receiveheader bytes to be added in each DTU, where header bytes may containsequence identification (SID) and/or time stamp information. The datamay then be sent to a cyclic redundancy check (CRC) calculationcomponent 212, a retransmission queue 210 and a multiplexor 213. The CRCcomponent 212 computes a CRC that can be inserted in the DTU to help thereceiver side improve error detection in the received data. The CRC maybe inserted in the DTU upon request from a receiver side (e.g., atinitialization time). The data sent to the retransmission queue 210 canbe stored for retransmission. The multiplexor 213 may multiplex togetherthe DTU framer 206 output data with the computed CRC from the CRCcomponent 212, and some dummy bytes (for padding). Then the multiplexor213 sends the multiplexed data across an alpha (α) to the PMS-TC layer208.

The data may then be sent across an alpha (a) interface 214 to thePMS-TC layer 208 at a scrambler component 216. The scrambler component216 can scramble the received data and send the scrambled data to aforward error correction (FEC) encoder 218. The FEC encoder 218 canencode the scrambled data and send the encoded data to an interleaver220, which sends the data to a multiplexor 222. The multiplexor 222multiplexes the data from the interleaver 220 with PMS-TC overhead data.The multiplexor 222 sends the multiplexed data across a delta (δ)interface 226 to a PMD layer 228 and on to a receiver side.

Also illustrated in FIG. 2A, is a retransmission control channel (RCC)decoder 224. More specifically, if a corrupted DTU is determined at thereceiver, the receiver can send a DTU status message to the RCC decoder224. The status message may be encoded to improve its robustness tointerference when transmitted over the line. The RCC decoder 224 decodesthe status messages received from the receiver, where the decodingprocess involves verifying the correctness of received message andextracting retransmission control data (e.g., which DTU needretransmission) from the message. Then the RCC decoder 224 sendsretransmission control data across the alpha layer 214 to theretransmission queue 210 to facilitate retransmission of the data.

FIG. 2B illustrates a receiver reference model for a DSL retransmissionmethod, with a rescheduling queue implemented in the TPS-TC layer. Asillustrated, the data from FIG. 2A may be received from a PMD layer 230,across a delta interface 232 at a PMS-TC layer 234 on a receiver side.The data may be received at a demultiplexor 236, which may separateoverhead data from payload data. The payload data may be sent to adeinterleaver 237, which deinterleaves the data and forwards the data toa FEC decoder 238. The FEC decoder decodes the payload data anddetermines whether there are uncorrectable errors in the data. If so, anindication that the FEC codeword contains incorrect data may be sentdirectly to a DTU error detector 248 on a TPS-TC layer 246. The FECdecoder output data is then sent to a descrambler 240, which descramblesthe data and sends the descrambled data across a beta (β) interface 244to the DTU error detector 248.

The DTU error detector 248 can determine if there are any errors in thereceived DTUs. Error detection can be done based on information receivedfrom the FEC decoder 238, and/or via checking the CRC (if any) embeddedin the DTU's padding bytes. If the receiver side has the ability tocheck the CRC in the error detector 248, the receiver may request (tothe transmitter side) insertion of a CRC in the DTU. If an error isdetected in the DTU, the DTU error detector 248 sends a retransmissionrequest for that particular DTU to a RCC encoder 242. The RCC encoder242 creates an RCC message, which is sent back to the transmitter, asdescribed in reference to FIG. 2A or FIG. 3A. If no error is detected,the DTU error detector 248 sends an acknowledgment for that particularDTU to a RCC encoder 242, then sends the data to a rescheduling queue250, and on to an upper layer, across a gamma interface 254.

FIG. 3A illustrates a transmitter reference model for a DSLretransmission method with the retransmission queue implemented in thePMS-TC layer. As illustrated in FIG. 3A, data may be sent from across agamma interface to a DTU framer component 306 in a TPS-TC layer 300. TheDTU framer component 306 can also receive header bytes and frame thereceived data and header bytes into one or more DTUs. Header bytes maycontain sequence identification (SID) and/or time stamp information foreach DTU. The data may then be sent to a cyclic redundancy check (CRC)calculation component 307 and a multiplexor 309. The CRC component 307computes a CRC that can be inserted in the DTU to improve errordetection in the received data at a receiver side. The CRC may beinserted in the DTU upon request from a receiver side (e.g., atinitialization time). The output data from the DTU framer 306 may bemultiplexed in the multiplexer device 309 with the output of the CRCcomponent 307 and some dummy bytes for padding. Output data from themultiplexor 309 may be sent across an alpha (a) interface 302 to ascrambler component 304 on a PMS-TC layer 208. The scrambler component304 can scramble the received data and send the scrambled data to aretransmission queue 310 for storage. Additionally, the DTUs (as well asretransmitted DTUs) may be sent to a FEC encoder 312 for encoding. Theencoded data may be sent to an interleaver 314. A multiplexor 316 maymultiplex data and PMS-TC overhead data for sending across a deltainterface 318 to a PMD layer, and on to a receiver.

Also illustrated in FIG. 3A, the PMD layer 320 can also receive afar-end RCC message for retransmission. This message may be sent to aRCC decoder 322, which formats the request to facilitate retransmissionof the data at the retransmission queue 310.

FIG. 3B illustrates a receiver reference model of a DSL retransmissionmethod with a rescheduling queue implemented in the PMS-TC layer. Asillustrated, a PMD layer 330 at a receiver can receive data and send thereceived data across a delta interface 332, to a demultiplexor 336 on aPMS-TC layer 334. The demultiplexor 336 can separate the PMS-TC overheaddata from the DTUs. The DTUs can be sent to a deinterleaver 338, whichdeinterleaves the data and sends the data to an FEC decoder 340. The FECdecoder 340 can then either detect FEC codeword errors in the receiveddata, or correct errors in the received data, or perform a combinationof both error detection and correction. Information regarding detectionof erroneous FEC codeword is sent to a DTU error detector 342.

The DTU error detector 342 can determine whether there are anyuncorrectable errors in the DTU and, if so, send a retransmissionrequest for the particular DTU to a RCC encoder 346. The RCC encoder 346can send an RCC message back to the transmitter, as described inreference to FIG. 2A or FIG. 3A. If the DTU error detector 342determines that there are no uncorrectable errors in the DTU, the FECdecoder output data is sent to a rescheduling queue 348, as well as adescrambler 350 for descrambling. The descrambled data can be sentacross a beta interface 352 to a TPS-TC layer 354.

FIG. 4A illustrates a DTU frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes as tail bytes at theend of the frame.

The basic frame is a block formed of and integer number of FECcodewords. Furthermore, the block contains an integer number of ATMcells spread about an integer number of FEC codewords, plus two or moreadditional bytes to provide sequence identification, tagging (e.g.,inclusion of a time stamp), error detection, etc.

In xDSL, the FEC code is a Reed-Solomon (RS) code that operates over theGalois Field GF(256). Therefore, one may also refer the DTU as an RSblock, since it is formed by an integer number of RS codewords.

In each DTU, there are M FEC codewords containing N_(fec) bytes each,where K bytes are the data bytes and R bytes are the redundancy bytes.

Two header bytes are defined for block identification and passing of atime stamp. Specifically, the first byte may define a SequenceIdentifier (SID) and the second byte may be used for passing of a timestamp (TS).

Padding bytes may also be included and defined for improved granularity(fitting an integer number of ATM cells into an integer number of FECcodewords) and/or error detection of the data bytes within the DTU.While the padding bytes may be implemented as tail bytes, at the end ofan ATM cell, this is a nonlimiting example, as the padding bytes mayresided at other places within the DTU frame structure.

Spread throughout the data fields in the block of FEC codewords are QATM cells. Each Block contains M FEC codewords, where each FEC codewordcontains K data bytes and R redundancy bytes.

In one possible configuration, the first ATM cell boundary immediatelyfollows two header bytes. Similarly, in the last codeword of each DTU,the last ATM cell is adjacent to the first padding byte.

Other configurations may operate with the padding bytes in a differentlocation, such as between the header bytes and the first AMT cell, asdepicted in FIG. 4B.

Additionally, one or more padding bytes may be defined for errordetection of the data bytes within the DTU.

The following equations define the number of bytes in the frame:

In each DTU, there are M·K=N_(header)+Q·53+N_(padding) bytes.

The total number of bytes in a DTU is M·N_(fec)=M·K+M·R.

Substituting the above two equations givesM·N _(fec) =N _(header) +Q·53+N _(padding) +M·R bytes.

The DTUs are transmitted at the line rate R_(line) (in Mbits per second)into DMT symbols. T_(RS) is the time duration (in seconds) of the FECcodeword, so

$R_{line} = {\frac{8 \cdot N_{fec}}{T_{RS}}.}$The FEC codewords are transported in DMT Symbols; T_(S) is the DMTsymbol period, so

$R_{line} = \frac{L_{p}}{T_{S}}$where L_(p) is the number of bits per DMT symbol. Combining the twoequations, the relation between the FEC codeword duration and the DMTSymbol period is T_(RS)=S·T_(S), where S is the number of DMT symbolsper FEC codeword and

$S = {\frac{8 \cdot N_{fec}}{L_{p}}.}$

If the retransmission and rescheduling queue management is performed inthe PMS-TC layer, then the fundamental units stored in the transmitterand receiver queues can be either data blocks of M·K bytes each, orblocks of M·(K+R) bytes each if storing the FEC redundancy.

If the retransmission and rescheduling queue management is performed inthe TPS-TC layer, then the fundamental units stored in the transmitterand receiver retransmission queues can be data blocks each formed of QATM cells. Header and padding bytes may not need to be stored in theretransmission and rescheduling queues.

The padding bytes may contain a CRC that spans all of the M·K data bytesin the DTU. By doing this, the system continues having a CRC on the datastream, as it exists in current xDSL solutions for the sake of keepingthe ability to detect errors on the data stream. However, while incurrent legacy xDSL systems, the CRC may be located at the superframelevel, in this embodiment, the CRC is located precisely at the DTUlevel.

The above CRC counts can be used as a primitive to compute erred secondsand severely erred seconds, which are metrics typically used formonitoring the quality of transmission

The following is an example configuration: Q=10 ATM Cells per FECcodeword block; M=3 codeword per FEC codeword block; N_(header)=2 bytes:the first byte for SID and the second byte for a TAG (e.g. time stamp);N_(padding)=2 bytes for a 16 bit CRC; R=16 bytes for FEC coderedundancy; M·K=2+10×53+2=534 data bytes per FEC codeword block; K=178bytes in each FEC codeword.

Note that the padding bytes may contain additional dummy bytes whenM·K≢N_(header)+Q·53+N_(crc) where N_(crc) is the number of CRC bytes inthe DTU. This helps to align the Q ATM cells with M FEC codewords.

At the transmitter, a scrambler device is used between the TPS-TC layerand the PMS-TC layer. The scrambler is reset at the beginning of eachDTU frame.

At the receiver, a descrambler device is used between the PMS-TC layerand the TPS-TC layer. The descrambler is reset at the beginning of eachDTU frame.

The retransmission control channel (RCC) may be implemented such that amessage is sent from the receiver to the transmitter within each DMTsymbol. The messages would provide an indication of the correctly andincorrectly received DTUs.

FIG. 4B illustrates a frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes at the beginning ofthe frame, after the header bytes. As illustrated in the nonlimitingexample of FIG. 4B, the padding bytes need not be located at the end ofthe frame structure. In at least one exemplary embodiment, the paddingbytes may be located between the header bytes and the first ATM cell (53bytes). Other embodiments are also contemplated.

FIG. 4C illustrates a frame structure for transport of asynchronoustransfer mode (ATM) cells for transparent retransmission management,such as may be utilized in the environment from FIGS. 2A, 2B, 3A, and3B, where the frame structure appends padding bytes at both thebeginning and end of the frame, after the header bytes. In at least oneexemplary embodiment, the padding bytes may be separated into twogroups, the first group between the header bytes and the first ATM cell(53 bytes) and the second group as tail bytes after the last ATM cell.As a nonlimiting example, the header padding bytes may be dummy bytes,and the tail padding bytes may be used to contain a CRC. Otherembodiments are also contemplated.

The 53 bytes ATM cells represented in FIGS. 4A 4B and 4C can be replacedwith other size cells such as for example 65 bytes fragment of a PTMprotocol.

FIG. 5 illustrates an example process that may be utilized forretransmission of data between a plurality of devices. As illustrated inthe nonlimiting example of FIG. 5, data may be framed into transportframes, each transport frame carrying payload data that is vieweddifferently according to the computing layer in which it is transported(block 550). Additionally, the transport frames may be transported overa first computing layer, the payload data of each transport framecorresponding to an integer number Q of elementary cells of the firstcomputing layer, an integer number of header bytes containinginformation specific to the transport frame, and an integer number ofpadding bytes (block 552). Similarly, the transport frames may betransported over a second computing layer, the payload data content ofeach transport frame corresponding to payload data of an integer numberM of elementary cells of the second computing layer (block 554).

Further, in some embodiments, a number of padding bytes is determinedsuch that a total number of bytes contained in the payload of the secondcomputing layer M elementary cells equals a total number of bytescontained in the header bytes plus padding bytes plus Q elementary cellsof the first computing layer.

The embodiments disclosed herein can be implemented in hardware,software, firmware, or a combination thereof. At least one embodimentdisclosed herein may be implemented in software and/or firmware that isstored in a memory and that is executed by a suitable instructionexecution system. If implemented in hardware, one or more of theembodiments disclosed herein can be implemented with any or acombination of the following technologies: a discrete logic circuit(s)having logic gates for implementing logic functions upon data signals,an application specific integrated circuit (ASIC) having appropriatecombinational logic gates, a programmable gate array(s) (PGA), a fieldprogrammable gate array (FPGA), etc.

One should note that the flowcharts included herein show thearchitecture, functionality, and operation of a possible implementationof software. In this regard, each block can be interpreted to representa module, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that in some alternativeimplementations, the functions noted in the blocks may occur out of theorder and/or not at all. For example, two blocks shown in succession mayin fact be executed substantially concurrently or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved.

One should note that any of the programs listed herein, which caninclude an ordered listing of executable instructions for implementinglogical functions, can be embodied in any computer-readable medium foruse by or in connection with an instruction execution system, apparatus,or device, such as a computer-based system, processor-containing system,or other system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device. The computer readable medium can be, for examplebut not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device. More specificexamples (a nonexhaustive list) of the computer-readable medium couldinclude an electrical connection (electronic) having one or more wires,a portable computer diskette (magnetic), a random access memory (RAM)(electronic), a read-only memory (ROM) (electronic), an erasableprogrammable read-only memory (EPROM or Flash memory) (electronic), anoptical fiber (optical), and a portable compact disc read-only memory(CDROM) (optical). In addition, the scope of the certain embodiments ofthis disclosure can include embodying the functionality described inlogic embodied in hardware or software-configured mediums.

One should also note that conditional language, such as, among others,“can,” “could,” “might,” or “may,” unless specifically stated otherwise,or otherwise understood within the context as used, is generallyintended to convey that certain embodiments include, while otherembodiments do not include, certain features, elements and/or steps.Thus, such conditional language is not generally intended to imply thatfeatures, elements and/or steps are in any way required for one or moreparticular embodiments or that one or more particular embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements and/or steps are included orare to be performed in any particular embodiment.

It should be emphasized that the above-described embodiments are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of this disclosure. Many variations andmodifications may be made to the above-described embodiment(s) withoutdeparting substantially from the spirit and principles of thedisclosure. Further, the scope of the present disclosure is intended tocover all combinations and sub-combinations of all elements, features,and aspects discussed above. All such modifications and variations areintended to be included herein within the scope of this disclosure.

Therefore, at least the following is claimed:
 1. A method forretransmission comprising: framing data into transport frames, eachtransport frame carrying payload data; transporting the transport framesover a first computing layer, the payload data of each transport framecorresponding to an integer number Q of elementary cells of the firstcomputing layer, an integer number of header bytes containinginformation specific to the transport frame, and an integer number ofpadding bytes; and transporting the transport frames over a secondcomputing layer different from the first computing layer, the payloaddata content of each transport frame corresponding to payload data of aninteger number M of elementary cells of the second computing layer,wherein a number of padding bytes is determined such that a total numberof bytes contained in the payload of the second computing layer Melementary cells equals a total number of bytes contained in the headerbytes plus padding bytes plus Q elementary cells of the first computinglayer.
 2. The method of claim 1, wherein the elementary cell of thefirst computing layer is an asynchronous transfer mode (ATM) cellcontaining 53 bytes.
 3. The method of claim 1, wherein the elementarycell of the first computing layer is a 65 bytes fragment from a packettransfer mode (PTM) protocol.
 4. The method of claim 1, wherein thesecond computing layer elementary cell is a forward error correction(FEC) codeword, formed by payload and redundancy bytes, wherein theredundancy bytes are generated from the payload bytes of a common cell.5. The method of claim 1, wherein payload data in the second computinglayer is a scrambled version of the payload data in the first computinglayer.
 6. The method of claim 1, wherein padding bytes contain one ormore dummy bytes, wherein the dummy bytes carry no useful information.7. The method of claim 1, wherein padding bytes contain one or morenon-dummy bytes, wherein the non-dummy bytes carry information that isuseful at at least one of the following: a transmitter side and areceiver side.
 8. The method of claim 7, wherein the non-dummy paddingbytes contain one or more bytes configured for facilitating detection oferroneous frames.
 9. The method of claim 8, wherein the bytes configuredfor facilitating detection of erroneous frames contain cyclic redundancycheck (CRC) information.
 10. The method of claim 1, wherein M and Q aredifferent integer numbers from each other.
 11. A system forretransmission, comprising: a transmitter side device that includes: afirst computing layer configured to transport first layer transportframes, the first layer transport fames including payload data, thepayload data of each transport frame corresponding to an integer numberQ of elementary cells of the first computing layer, an integer number ofheader bytes containing information specific to the transport frame, andan integer number of padding bytes, and a second computing layerdifferent from the first computing layer, the second computing layerconfigured to transport second format transport frames, the payload datacontent of each second format transport frame corresponding to aninteger number M of elementary cells of the second computing layer,wherein a number of padding bytes is determined such that the totalnumber of bytes contained in the payload of the second computing layer Melementary cells equals the total number of bytes contained in theheader bytes plus padding bytes plus Q elementary cells of the firstcomputing layer.
 12. The system of claim 11, wherein padding bytescontain one or more dummy bytes, wherein the dummy bytes carry no usefulinformation.
 13. The system of claim 11, wherein padding bytes containone or more non-dummy bytes, wherein the non-dummy bytes carryinformation that is useful at at least one of the following: atransmitter side and a receiver side.
 14. The system of claim 11,wherein the transport frame structure includes one or more padding bytesconfigured for facilitating detection of erroneous frames.
 15. Thesystem of claim 14, wherein the bytes configured for facilitatingdetection of erroneous frames carrying cyclic redundancy check (CRC)information.
 16. The system of claim 11, wherein a number, location inthe transport frame, and type of padding bytes is at least partiallyindicated by a receiver side.
 17. The system of claim 11, wherein M andQ are different integer numbers from each other.
 18. A system forretransmission, comprising: a receiver side device that includes a datareceiving component configured to receive data from a transmitter sidedevice, the data including one or more retransmission transport framestructures being received over a second computing layer, then over afirst computing layer different from the second computing layer, whereinon the second computing layer, payload data of the transport framecorresponds to an integer number M of elementary cells of the secondcomputing layer, wherein on the first computing layer, the payload dataof the transport frame corresponds to an integer number Q of elementarycells of the first computing layer, an integer number of header bytescontaining information specific to the transport frame, and an integernumber of padding bytes, and wherein a number of padding bytes isdetermined such that a total number of bytes contained in the payload ofthe second computing layer M elementary cells equals the total number ofbytes contained in the header bytes plus padding bytes plus Q elementarycells of the first computing layer.
 19. The system of claim 18, whereinpadding bytes contain one or more non-dummy bytes, wherein the non-dummybytes carry information that is used by the receiver.
 20. The system ofclaim 18, wherein the transport frame structure includes one or morepadding bytes configured for facilitating error detection.
 21. Thesystem of claim 20, wherein the bytes configured for facilitatingdetection of erroneous frames carrying cyclic redundancy check (CRC)information.
 22. The system of claim 18, wherein a number, location inthe transport frame, and type of padding bytes to insert in eachtransport frame are at least partially indicated to a transmitter side.23. The system of claim 18, wherein M and Q are different integernumbers from each other.